The present invention relates to rackets for playing tennis, squash, badminton, racketball, or other games.
Conventional games rackets which are currently used, and are commercially available, have their playing surfaces formed by opposite sides of a single set of interwoven, tensioned stringing lying in a single median or central plane of the head frame of the racket, and spanning the central opening bounded by the head frame.
It has previously been proposed to replace the single central set of interwoven stringing by two sets disposed in generally parallel planes spaced apart by a distance approximating the thickness of the head frame. Such a "double-strung" racket construction possesses significant advantages over the conventional "centrally-strung" rackets. Particularly advantageous constructions of "double-strung" rackets form the subject of my U.S. Pat. No. 4,049,269 and U.S. patent application No. 895,021.
The invention is particularly concerned with such "double-strung" rackets, and specifically with the manner in which they are strung.
A major problem which has faced the racket industry for perhaps as long as 100 years is how to eliminate, or improve upon, the laborious operation of stringing conventional "centrally-strung" rackets, and a similar problem arises in connection with double-strung rackets. In order to achieve the required degree of tension and resilience in the stringing of, for example, a conventionally strung tennis racket, the stringing must, of necessity, take the form of a mesh woven from a filamentary material, i.e. single or composite filaments of natural gut or synthetic fibres. The mesh is composed of a first group of generally parallel string portions, and a second group of generally parallel string portions extending generally perpendicular to, and interwoven with, the string portions of the first group. The string portions (hereinafter referred to as the "mains") in one group usually extend generally parallel to the longitudinal axis of the handle or shaft of the racket, with the string portions (hereinafter referred to as the "crosses") in the other group extending generally transverse to that axis.
Stringing is usually effected by fitting the head frame onto a stringing machine, threading a stringing filament through stringing-receiving apertures in the head frame, back and forth across the central opening, to string the mains to the required tension, and then similarly stringing and tensioning the crosses, with the crosses woven between the mains. The mains are usually formed from one length of stringing filament, whilst the crosses are formed from another length.
This process possesses the disadvantage that it is relatively time-consuming. One of the most time-consuming aspects is the threading and weaving of the crosses, particularly since it is also necessary to pull through the relatively long unused portion or tail of the stringing filament as threading and weaving progresses.
Another disadvantage of conventional stringing processes, which stems from the foregoing, is that the stringing filaments are prone to damage due to friction between the stringing filaments which gives rise to scorching or burning, particularly when the crosses are pulled through the mains. However, unless the crosses are pulled through the mains relatively quickly, stringing becomes an even slower process.
A further disadvantage is that, as each stringing filament is threaded through an associated stringing-receiving aperture after forming each main or cross, it is tensioned, and this tension must be maintained temporarily by clamps, awls or other anchorages. As a result of these temporary anchorages, the stringing filaments are prone to damage at numerous places along their length during stringing.
Yet another disadvantage of existing stringing processes is that they apply, and are only capable of applying, substantially the same tension to all the mains and crosses, irrespective of their differing lengths. Thus, the resilience of the relatively short string portions, for example the peripheral crosses located adjacent the throat or shaft, will be substantially less than the resilience of the relatively long string portions, for example the central crosses located half-way between the throat and tip of the head frame, which are approximately twice the length of the former peripheral crosses.
Still another disadvantage of existing stringing processes is that they require a racket to be held rigidly in a relatively large and bulky metal framework to avoid distortion of the head frame during stringing.
My aforesaid patent and application both disclose a double-strung games racket, i.e. a racket having a head-frame across the central opening of which extend two sets of tensioned stringing, with each set being disposed in a respective one of two spaced generally parallel planes, the stringing passing through stringing-receiving apertures distributed around the periphery of the frame and opening at their outer ends into opposite side surfaces of the frame, i.e. surfaces which are spaced apart in a direction generally normal to the planes of the stringing.
The apertures are isolated from the outer periphery of the frame by the material of the frame, and the stringing is effected by threading filaments through the apertures to produce the two sets of interwoven mains and crosses in a manner somewhat analagous to that previously described. The stringing technique is therefore prone, to a certain degree, to at least some of the aforementioned disadvantages.
It is an object of the present invention to provide a stringing technique for double-strung rackets which overcomes, or substantially reduces, at least some of the aforementioned disadvantages.
The frame of the double-strung racket disclosed in my aforesaid application is formed, in its outer periphery, with a channel extending around the central opening, the stringing-receiving apertures, intermediate their outer ends, opening into the channel. The channel serves to accommodate interconnecting portions of the stringing filaments which connect the set of stringing in one plane to the set in the other plane.